Significance of Brooding to the Energy Demands of Alaskan Rock Ptarmigan Chicks

Abstract

Rock ptarmigan (Lagopus mutus) chicks are brooded periodically during the first few days of life; longer in cold and rainy weather. Computed minimum foraging time in adverse weather conditions is 96 minutes/24 hours. Crop analysis and calorimetry of the 6 major food items show that a full crop may contain up to 0.47 kcals. Energy requirements were calculated for both an 18-gram chick and a 30-gram chick. The 18-gram chick required between 34 and 50 crop loads per 24 hours. With 96 minutes foraging time, and the observed pecking rates, this was considered possible. The 30-gram chick required twice as much foraging time but since it was approaching homeothermy, it was tentatively concluded that neither was that chick being handicapped by brooding. Vagaries in early survival of rock ptarmigan chicks, therefore, are not due to differences in post-hatch weather.